| 摘要 |
<p>A variable gain amplifier has a first amplifier circuit (1) whose gain is A/n times (A being a real number excepting "0", and n being a real number larger than 1); a second amplifier circuit (2) whose gain is A(n-1/n) times; level converter (3) for level converting an output signal from the second amplifier circuit at a ratio corresponding to a level of a gain control signal (VGC) having a predetermined level controllable range and at a ratio of 1/(n+1) at a central level (VGCCEN) within the level controllable range of the gain control signal; and an adder circuit (4) for adding together an output signal from the level converter (3) and an output signal from the first amplifier circuit (1) at the ratio of 1:1. The variable gain amplifier has a gain controllable range of among 1/n SIMILAR 1 SIMILAR n times as the level of the gain control signal changes among the minimum level (VGCMIN) SIMILAR the central level (VGCCEN) SIMILAR the maximum level (VGCMAX). When the gain of the second amplifier circuit (22) is set to A(m-1/n) times (m being a real number larger than 1) and a level conversion ratio of the level converter (23) is set to (1-1/n)/(m-1/n) at the central level of the gain control signal (V23), the variable gain amplifier having the gain controllable range of among A/n - A - mA times is realized. <IMAGE></p> |
